Sample handing tools having a plurality of pipetting devices are widely used, for example in proteomic and genomic research and in laboratory and clinical procedures which require a predetermined amount of material to be taken from one work area and dispensed on another work area. These devices are used to move material samples both to and from a variety of different types of work areas, such as microtiter trays, gels having separated DNA fragments, and other material holding devices. Some such tools may have a plurality of pipetting devices arranged in an array that corresponds to wells in a microtiter tray, such as the commonly-known 96-well or 384-well plate. This arrangement may allow material to be simultaneously deposited in, and removed from, wells in the microtiter tray, thus increasing the speed at which a plurality of samples in a microtiter tray are processed.
The pipetting devices in the tool typically include a plunger or piston that moves within a channel. The plunger may be actuated in one direction to draw fluid into the channel, e.g., to cause aspiration of a sample at a corresponding needle or pipette tip, and in the opposite direction to discharge fluid from the channel, e.g., to dispense a sample. A seal is typically provided between the plunger and channel to create a pressure differential as the plunger is moved in the channel. Commonly, the plunger is made with a highly polished or otherwise smooth surface, and forms a seal with an O-ring or other member mounted on the channel. The integrity of the seal is important to being able to draw and discharge material into and from the pipette. Thus, a longer useful life and reliability for the seal is desirable.